Diagnostic Categories of Incontinence and the Role of Urodynamic Testing

rinary incontinence is the result of an imbalance between the maximum intravesical pressure and the maximum urethral pressure U at any given time except during normal voiding. Any combination that brings about an excess of intravesical pressure over the maximum urethral pressure will result in urine loss. Such combinations are outlined in Table 1. This simplified table does not necessarily indicate that a rise in intravesical pressure or a drop in urethral pressure equates to urinary incontinence. In many cases, specifically in the elderly, multiple factors may be involved and may together produce an imbalance that may lead to urinary incontinence. The uninhibited detrusor contraction (UDC) regardless of etiology must be of sufficient force to break through the urethral lumen to produce urinary incontinence. Urine loss, therefore, in patients with UDC will depend on the status of the urethral sphincters at the time of the occurrence of the UDC. Passive increase of bladder pressure may be observed in patients with overdistended bladders. Bladder wall compliance may be normal or even increased, such that overflow incontinence occurs at very large bladder volumes. This is in contrast to bladders with reduced compliance where urine loss may occur at low volumes. In cases of unstable urethra, the urethral pressure drop is considered an inappropriate response (relaxation) of the urethral sphincter to either a detrusor contraction or detrusor stretching without measurable detrusor contraction. An appropriate normal response to bladder wall stretching or to an involuntary detrusor contraction is contraction of the periurethral striated muscle. The exact etiology of this entity is still poorly understood. The loss or reduction of urethral compliance may lead